BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an image developer and to image forming apparatuses,
particularly to copiers, facsimiles, printers and complex machines having these functions
using electrophotographic processes.
Discussion of the Background
[0002] Recently, stable image quality which is free from uneven image density even when
high-density or full-color images having a large image area are continuously produced
is demanded.
[0003] Therefore, the image developer needs to separate and collect the developer from the
developer bearer (herein after referred to as a developing sleeve) after producing
images having a large image area consuming a large amount of the toner, feed the toner
to the developer and uniformly disperse the toner therein to resume the original toner
concentration, and quickly feed the developer to the developing sleeve.
[0004] However, in a conventional image developer as shown in Fig. 7, since a part separating
the developer used for the development from the developing sleeve 2 and collecting
the developer to a developer feeder 11 (hereinafter referred to as a screw) is close
to a part feeding the new developer to the developing sleeve, the used developer is
fed to the developing sleeve 2 again without a new toner, resulting in uneven image
density.
[0005] In addition, since the collected developer and the developer being fed are mixed
in a same section 13, the developer is difficult to have a uniform toner concentration
between upstream and downstream sides of the screw 11 in Fig. 8. The developer has
less toner concentration downstream and images having uneven image density in the
longitudinal direction of the developing sleeve 2 are likely to be produced.
[0006] As shown in Figs. 5 and 6, Japanese published unexamined patent application No.
5-333691 discloses a marketed functionally-separated image developer in which a screw and
a feed route having been laterally located are vertically located to separate sections
of feeding and collecting the developer, i.e., the developer is separated and collected
by a lower screw 5 at a section 8 and the developer is fed by an upper screw 4 at
a section 7.
[0007] However, at a communicating route D where the lower screw 5 transfers the developer
to the screw 4, the developer needs to be deposited and the developer is fed from
the section 8 to the section 7, i.e., the used developer is directly fed to the developing
sleeve 2 again, resulting in uneven image density.
[0008] In addition, only the lower and upper screws do not fully stir the developer, resulting
in uneven image density and deterioration of image density. Japanese published unexamined
patent application No.
11-167260 discloses an image developer as shown in Figs. 3 and 4, further including a section
9 besides the sections 7 and 8, having a stirrer 6 mixing and dispersing the collected
developer and a toner fed from T to improve uniformity of the image density.
[0009] The two screws vertically located in Figs. 5 and 6 save space more than the conventional
two screws laterally located. However, as mentioned above, the developer deposited
is fed to the developing sleeve again or is not well mixed with a newly-fed toner,
i.e., the developer is not fully stirred, resulting in uneven image density and deterioration
of image density.
[0010] In order to solve this problem, three screws are effectively located as shown in
Fig. 3. The developer needs to be deposited at a stirring detour 9 apart from the
developing sleeve, the low-concentration developer just after being collected not
being fed to the developing sleeve again. Further, the collected developer and a newly-fed
toner are sufficiently stirred at the stirring detour 9, which improves uneven image
density.
[0011] On the other hand, the image developer has a toner concentration sensor detecting
a concentration of the developer. This is typically a sensor detecting a magnetic
permeability of the developer and detects a toner concentration of a specific amount
of the developer close thereto. The sensor power and the toner concentration have
a linear relationship to each other, and the sensor detects excess and deficiency
of the toner to drive or stop a feeder of the developer.
[0012] In order to detect whether a proper amount of the toner is fed, it is necessary to
detect the developer fully dispersed and mixed and a specific distance is required
between a position from which the toner is fed and a position where the toner concentration
is detected.
[0013] However, it is impossible to reduce the toner from or add the toner to the developer
between these positions even when the toner is excessively or insufficiently fed from
the position from which the toner is fed. Therefore, the developer has a part having
a high toner concentration and a part having a low toner concentration while being
stirred and transferred, resulting in uneven image density after all.
[0014] In addition, polymerization toners frequently used lately are difficult to mix and
disperse in image developers due to their shapes. This is because the polymerized
toner having the shape of almost a sphere and a small particle diameter takes more
time to mix with a developer in the image developer than conventional pulverization
toners having a large particle diameter.
[0015] The toner concentration detector typically measures the concentration of the toner
in a developer fully mixed. However, when the developer insufficiently mixed is detected,
excessive toner feeding is repeated, resulting in toner scattering, background fouling
and uneven image density.
[0016] Because of these reasons, a need exists for an image developer and an image forming
apparatus capable of improving the dispersibility of a developer even including a
toner having poor mixability and dispersibility, and precisely detecting the toner
concentration to prevent uneven toner concentration of the developer and uneven image
density.
SUMMARY OF THE INVENTION
[0017] Accordingly, an object of the present invention is to provide an image developer
capable of improving the dispersibility of a developer even including a toner having
poor mixability and dispersibility,and precisely detecting the toner concentration
to prevent uneven toner concentration of the developer and uneven image density.
[0018] Another object of the present invention is to provide an image forming apparatus
using the image developer. These objects and other objects of the present invention
have been satisfied by an image developer as defined in claim 1.
[0019] These and other objects, features and advantages of the present invention will become
apparent upon consideration of the following description of the preferred embodiments
as defined in the dependent claims, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Various other objects, features and attendant advantages of the present invention
will be more fully appreciated as the same becomes better understood from the detailed
description when considered in connection with the accompanying drawings in which
like reference characters designate like corresponding parts throughout and wherein:
Fig. 1 is a schematic view illustrating a cross-section of the image developer of
the present invention, and of a photoreceptor;
Fig. 2 is an explanatory drawing of the developer circulation of the present invention;
Fig. 3 is a schematic view illustrating a known cross-section of an image developer
having a detour transfer route, and of a photoreceptor;
Fig. 4 is an explanatory drawing of the developer circulation in Fig. 3;
Fig. 5 is a schematic view illustrating a cross-section of a conventional image developer
having vertically-located two screws, and of a photoreceptor;
Fig. 6 is an explanatory drawing of the developer circulation in Fig. 5;
Fig. 7 is a schematic view illustrating a cross-section of a conventional image developer,
and of a photoreceptor;
Fig. 8 is an explanatory drawing of the developer circulation in Fig. 7;
Fig. 9 is a schematic view for explaining a shape of a toner;
Fig. 10 is a schematic view for explaining a shape of the toner; and
Figs. 11A to 11C are schematic views for explaining a shape of the toner.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The present invention provides an image developer capable of improving the dispersibility
of a developer even including a toner having poor mixability and dispersibility, and
precisely detecting the toner concentration to prevent uneven toner concentration
of the developer and uneven image density. More particularly, the present invention
relates to an image developer, comprising:
a developer bearer configured to be rotatable facing an electrostatic latent image
bearer;
a developer feeder configured to feed a developer comprising a toner to the developer
bearer;
a developer collector configured to collect the developer which is left on the developer
bearer after the developer is fed to the electrostatic latent image bearer and which
is then separated from the developer bearer;
a detour route configured to stir the developer and transfer the developer from the
developer feeder to the developer collector;
a first opening configured to connect the developer feeder with the detour route;
a second opening configured to connect the detour route with the developer collector;
and
a third opening configured to connect to a developer supplier, configured to supply
the developer to the image developer,
wherein the image developer further comprises a detector configured to detect a toner
concentration of the developer, wherein the detector is located on a downstream side
of the developer collector and on an upstream side of the second opening (A).
[0022] An embodiment of the present invention will be explained, referring to Figs. 1 and
2.
[0023] Fig. 1 is a schematic view illustrating a cross-section of the image developer of
the present invention, and of a photoreceptor. First, the surface of a rotatable photoreceptor
10 is uniformly charged with a charger (not shown). Next, information based on an
original read with an image reader (not shown) or information from a host PC is written
thereon with a laser beam from a laser writer (not shown) to form an electrostatic
latent image thereon.
[0024] An image developer 1 includes a rotatable developing sleeve 2 including a magnetic
material (not shown) and uniformly feeding a toner to the photoreceptor 10 to visualize
the electrostatic latent image. The magnetic material holds a developer on the developing
sleeve 2, and a doctor blade 3 regulates an amount thereof to be held.
[0025] The doctor blade 3 is mostly a plate such as a stainless steel plate leaving from
the developing sleeve 2 at a distance of 0.2 to 1.2 mm to form a uniform thin layer
of the developer thereon and uniformly feed the developer to the electrostatic latent
image on the photoreceptor 10 without irregularities.
[0026] The image developer 1 is filled with a developer, and a consumed developer is replaced
with a new developer in many cases. A feeder feeding a new developer and a collector
separating and collecting a consumed developer are required close to the doctor blade.
In order to separate a consumed developer, the magnetic material in the developing
sleeve 2 is partially demagnetized.
[0027] Next, the developer movement in the image developer 1 will be explained. The feeder
feeding the developer close to the developing sleeve 2 and doctor blade 3 has the
shape of a paddle capable of boosting and flipping up, and has the shape of a screw
laterally transferring the developer as shown in Fig. 2 in the present invention.
[0028] The collector collecting a separated developer also has the shape of a paddle to
quickly scrape up the developer, and preferably has the shape of a screw to transfer
the developer in the axial direction of the developing sleeve 2.
[0029] In Fig. 2,a developer is fed from a feeding screw 4 to the developing sleeve 2, the
developer after being used for developing separates and leaves therefrom and is collected
by a collection screw 5 as indicated by an arrow. The developer separated from the
developing sleeve 2 is preferably collected quickly.
[0030] A difference with a conventional image developer is using screws independently for
feeding and collecting the developer. In Figs. 7 and 8, only a single screw 11 transfers
the developer to a developing sleeve 2. In Figs. 7 and 8, an excessive developer from
a first transfer (feeding) route and a collection developer from a second transfer
(collection) route are united, stirred and circulated to the first transfer (feeding)
route through a third transfer (stirring detour) route. The developer circulated to
the first transfer (feeding) route has a more uniform concentration of the toner,
and high-quality images having a constant image density without uneven image density
can be produced even when having a high image area. The conventional image developer
has the same structures as the present invention in respect of a first transfer (feeding)
route, a second transfer (collection) route and a third transfer (stirring detour)
route. Three openings located on a downstream side of the feeding route to the stirring
detour, from the collection route to the stirring detour, and from the stirring detour
to the feeding route respectively are same as well. However, the conventional image
developer has a toner concentration detector at the third transfer (stirring detour)
route, different from the preferred downstream side of the second transfer (collection)
route of the present invention.
[0031] The conventional image developer has an opening for feeding toner on a downstream
side of the first transfer (feeding) route and a toner concentration sensor detects
the concentration of the developer after the toner is fed to, which is largely different
from detecting the concentration of the developer before the toner is fed to of the
present invention.
[0032] In the image developer 1 in Figs. 1 and 2, the feeding screw 4 and collection screw
5 are separately located to perform independent functions. A housing of the image
developer is located surrounding the feeding screw 4 and has a slit-shaped opening
accommodating the doctor blade 3 and the developing sleeve 2 to form a section 7 therein.
Similarly, the housing is located surrounding the collection screw 5 and has a slit-shaped
opening to the surface of the developing sleeve 2 to form a section 8 therein.
[0033] The developer present at the sections 7 and 8 needs replacing in use. The conventional
image developer in Figs. 5 and 6 has communicating openings of D and E through which
the developer directly comes in and out. In order to transfer the developer from the
section 8 to the section 7, the developer needs depositing at the section 8. The developer
is deposited at the opening D in Fig. 6, i.e., on a lowermost downstream side of the
collection screw 5 and is transferred to the feeding screw 4.
[0034] However, when the deposited developer reaches the inside of the axial direction of
the developing sleeve 2 shown in Fig. 6, i.e., an image area, the collection section
8 shown in Fig. 5 is filled with the developer and the developer directly enters the
feeding section 7 along the surface of the developing sleeve 2 without passing the
opening D. Most of the developer passes through the doctor blade, resulting in uneven
image density. As shown in Figs. 3 and 4, the detour transfer section 9 is located
between the collection section 8 and the feeding section 7, in which the developer
deposits to prevent the deposited developer from being fed to the developing sleeve
2 again. In Figs. 3 and 4, a stirring screw 6 is located in the detour transfer section
to lengthen a stirring distance as long as possible because of preventing uneven image
density due to insufficient mixing of the toner with the collected developer. In addition,
it is suggested that the stirring distance is further extended with four screws in
order to improve stirring performance.
[0035] In Figs. 3 and 4, a feeding opening T of the toner fed from a feeder (not shown)
is located at the farthest distance from an opening B just before feeding the developer
to the developing sleeve, and a toner concentration sensor 15 is located at the farthest
distance from the feeding opening where the developer deposits, i.e., close to the
opening B where the developer is lifted up to the screw above.
[0036] This is because the toner sensor 15 is located close to the opening B to detect the
developer sufficiently stirred. In the present invention, as shown in Fig. 1, the
toner concentration sensor 15 is located on a downstream side of the developer collection
screw 5, which detects the developer before a new toner is fed thereto and an amount
of the toner consumed, to feed just a necessary amount thereof to the image developer
through the feeding opening T. Therefore, in the present invention, the toner concentration
before the toner is fed to the developer is detected, which is largely different from
the conventional detection of the toner concentration after the toner is fed to the
developer. It is not necessary to detect the toner concentration after the toner is
fed thereto and it is necessary to precisely detect the toner concentration before
the toner is fed thereto without delay. In addition, in the present invention, the
image developer 1 includes three screws.
In the conventional image developer in Fig. 7, the developer used for developing is
mixed with the other developer just after separating and leaving from the developing
sleeve 2. Therefore, it is impossible to detect the toner concentration before the
toner is fed to the developer, and the toner feeding is controlled with the concentration
thereof when the developer is mixed as above. For example, when images have a low
image area, the toner is consumed less and the image density varies less. However,
images having a large image area consume the toner more and the toner concentration
in the image developer 1 partially differentiates, resulting in uneven image density.
Conventionally, the toner consumption is forecasted from an image area and the toner
is fed to the image developer to prevent uneven image density. However, it is complicated
to control feeding the toner thereby. In the image developer vertically including
two screws, a toner feeding opening T is located at a downstream end of the developer
feeding screw 4, as shown in Fig. 6.
[0037] However, the new developer is mixed with the collected developer, and the toner concentration
of the developer before the toner is fed thereto is difficult to detect. Therefore,
the toner concentration of the developer after the toner is fed thereto is detected.
[0038] The image developer 1 using three screws will be explained. As shown in Fig. 2, the
feeding screw 4 and collection screw 5 are located parallel to the developing sleeve
2, and the screws 4 and 5 transfer the developer in the axial direction of the developing
sleeve 2.
[0039] The detour transfer screw 6 transfers the developer in the direction opposite to
those of the feeding screw 4 and collection screw 5. On the lowermost downstream side
of the detour transfer screw 6, the developer needs transferring to the feeding section
7 where the feeding screw 4 is located through an opening B after depositing in the
detour transfer section 9. A space between the detour transfer screw 6 and a developer
container is as small as possible, i.e., the detour transfer section 9 is so formed
as to surround the outer circumference of the screw, which effectively transfer the
deposited developer.
[0040] In the image developer including three functionally-independent screws, i.e., the
feeding screw 4, the collection screw 5 and the stirring transfer screw 6, the toner
concentration sensor 15 detects the toner consumption, i.e., an amount of the toner
required on a downstream side of the collection screw 5 to drive a toner feeder in
real time. Therefore, the developer in the stirring transfer section 9 and the stirring
transfer screw 6 has a stable toner concentration.
[0041] In combination with the conventional art of the location of the toner concentration
sensor, the present invention largely improves uneven image density without using
the complicated forecast of the toner consumption based on the image area.
[0042] This is not only the case where the feeding screw is above the collection screw,
but also the case where the collection screw is above the feeding screw.
[0043] Next, a toner preferably used in the present invention will be explained. The toner
preferably has a volume-average particle diameter of from 3 to 8 µm to produce an
image of 600 dpi. The toner preferably has a ratio (Dv/Dn) of the volume-average particle
diameter thereof to a number-average particle diameter thereof of from 1.00 to 1.40.
The closer to 1.00, the sharper the particle diameter distribution.
[0044] Although such a toner having a small particle diameter and a sharp particle diameter
distribution has uniform charge quantity distribution and high transferability, and
produces high-quality images with less background fouling, the toner has slightly
poor mixability and dispersibility with a developer in an image developer and is likely
to produce images having uneven image density.
[0045] Coulter Counter TA-II and Coulter Multisizer II from Beckman Coulter Inc. are used
for measuring the particle diameter distribution as follows:
0.1 to 5 ml of a detergent, preferably alkylbenzene sulfonate is included as a dispersant
in 100 to 150 ml of the electrolyte ISOTON R-II from Coulter Scientific Japan, Ltd.,
which is a NaCl aqueous solution including an elemental sodium content of 1%;
2 to 20 mg of a toner sample is included in the electrolyte to be suspended therein,
and the suspended toner is dispersed by an ultrasonic disperser for about 1 to 3 min
to prepare a sample dispersion liquid; and
a volume and a number of the toner particles for each of the following channels are
measured by the above-mentioned measurer using an aperture of 100 µm to determine
a weight distribution and a number distribution:
2.00 to 2.52 µm; 2.52 to 3.17 µm; 3.17 to 4.00 µm; 4.00 to 5.04 µm; 5.04 to 6.35 µm;
6.35 to 8.00 µm; 8.00 to 10.08 µm; 10.08 to 12.70 µm; 12.70 to 16.00 µm; 16.00 to
20.20 µm; 20.20 to 25.40 µm; 25.40 to 32.00 µm; and 32.00 to 40.30 µm.
[0046] The toner preferably has a shape factor SF-1 of from 100 to 180, and a shape factor
SF-2 of from 100 to 180.
[0047] Figs. 9 and 10 are schematic views illustrating shapes of toners for explaining shape
factors SF-1 and SF-2. The shape factor SF-1 represents a degree of roundness of a
toner, and is determined in accordance with the following formula (1):
wherein MXLNG represents an absolute maximum length of a particle and AREA represents
a projected area thereof.
[0048] When the SF-1 is 100, the toner has the shape of a complete sphere. As SF-1 becomes
greater, the toner becomes more amorphous.
[0049] SF-2 represents the concavity and convexity of the shape of the toner, and specifically
a square of the peripheral length of an image projected on a two-dimensional flat
surface (PERI) is divided by an area of the image (AREA) and multiplied by 100 π/4
to determine SF-2 as the following formula (2) shows.
[0050] When SF-2 is 100, the surface of the toner has less concavities and convexities.
As SF-2 becomes greater, the concavities and convexities thereon become more noticeable.
[0051] The shape factors are measured by photographing the toner with a scanning electron
microscope (S-800) from Hitachi, Ltd. and analyzing the photographed image of the
toner with an image analyzer Luzex III from NIRECO Corp.
[0052] When the shape of a toner is close to a sphere, the toner contacts the other toner
or a photoreceptor at a point. Therefore, the toners adhere less each other and have
higher fluidity. In addition, the toner and the photoreceptor adhere less to each
other, and transferability of the toner improves. When SF-1 or SF-2 is more than 180,
the transferability thereof deteriorates.
[0053] The toner preferably used for the image forming apparatus of the present invention
is formed by a crosslinking and/or an elongation reaction of a toner constituent liquid
including at least polyester prepolymer having a functional group including a nitrogen
atom, polyester, a colorant, a charge controlling agent and a release agent dispersed
in an organic solvent in an aqueous medium. Hereinafter, the toner constituents will
be explained.
[0054] The polyester is formed by polycondensating a polyol compound and a polycarboxylic
compound.
[0055] As the polyol (PO), diol (DIO) and triol (TO) can be used, and the DIO alone or a
mixture of the DIO and a small amount of the TO is preferably used. Specific examples
of the DIO include alkylene glycol such as ethylene glycol, 1,2-propylene glycol,
1,3-propylene glycol, 1,4-butanediol, and 1,6 -hexanediol; alkylene ether glycol such
as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol,
polypropylene glycol and polytetramethylene ether glycol; alicyclic diol such as 1,4-cyclohexanedimethanol
and hydrogenated bisphenol A; bisphenol such as bisphenol A, bisphenol F and bisphenol
S; adducts of the above-mentioned alicyclic diol with an alkylene oxide such as ethylene
oxide, propylene oxide and butylene oxide; and adducts of the above-mentioned bisphenol
with an alkylene oxide such as ethylene oxide, propylene oxide and butylene oxide.
In particular, alkylene glycol having 2 to 12 carbon atoms and adducts of bisphenol
with an alkylene oxide are preferably used, and a mixture thereof is more preferably
used. Specific examples of the TO include multivalent aliphatic alcohol having 3 to
8 or more valences such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol
and sorbitol; phenol having 3 or more valences such as trisphenol PA, phenolnovolak,
cresolnovolak; and adducts of the above-mentioned polyphenol having 3 or more valences
with an alkylene oxide. As the polycarbonate (PC), dicarboxylic acid (DIC) and tricarboxylic
acid (TC) can be used. The DIC alone, or a mixture of the DIC and a small amount of
the TC are preferably used. Specific examples of the DIC include alkylene dicarboxylic
acids such as succinic acid, adipic acid and sebacic acid; alkenylene dicarboxylic
acid such as maleic acid and fumaric acid; and aromatic dicarboxylic acids such as
phthalic acid, isophthalic acid, terephthalic acid and naphthalene dicarboxylic acid.
[0056] In particular, alkenylene dicarboxylic acid having 4 to 20 carbon atoms and aromatic
dicarboxylic acid having 8 to 20 carbon atoms are preferably used. Specific examples
of the TC include aromatic polycarboxylic acids having 9 to 20 carbon atoms such as
trimellitic acid and pyromellitic acid. PC can be formed from a reaction between the
PO and the above-mentioned acids anhydride or lower alkyl ester such as methyl ester,
ethyl ester and isopropyl ester. The PO and PC are mixed such that an equivalent ratio
( [OH] / [COOH] ) between a hydroxyl group [OH] and a carboxylic group [COOH] is typically
from 2/1 to 1/1, preferably from 1.5/1 to 1/1, and more preferably from 1.3/1 to 1.02/1.
The polycondensation reaction between the PO and PC is performed by heating the Po
and PC at from 150 to 280°C in the presence of a known esterification catalyst such
as tetrabutoxytitanate and dibutyltinoxide and removing produced water while optionally
depressurizing to prepare polyester having a hydroxyl group. The polyester preferably
has a hydroxyl value not less than 5, and an acid value of from 1 to 30 and more preferably
from 5 to 20.
[0057] When the polyester has an acid value within the range, the resultant toner tends
to be negatively charged to have good affinity with a recording paper and low-temperature
fixability of the toner on the recording paper improves. However, when the acid value
is greater than 30, the resultant toner is not stably charged and the stability becomes
worse by environmental variations. The polyester preferably has a weight-average molecular
weight of from 10, 000 to 400, 000, and more preferably from 20,000 to 200,000. When
the weight-average molecular weight is less than 10,000, offset resistance of the
resultant toner deteriorates. When greater than 400,000, low-temperature fixability
thereof deteriorates. The polyester preferably includes a urea-modified polyester
besides an unmodified polyester formed by the above-mentioned polycondensation reaction.
The urea-modified polyester is formed by reacting a polyisocyanate compound (PIC)
with a carboxyl group or a hydroxyl group at the end of the polyester formed by the
above-mentioned polycondensation reaction to form a polyester prepolymer (A) having
an isocyanate group, and reacting amine with the polyester prepolymer (A) to crosslink
and/or elongate a molecular chain thereof.
[0058] Specific examples of the PIC include aliphatic polyisocyanate such as tetramethylenediisocyanate,
hexamethylenediisocyanate and 2,6-diisocyanatemethylcaproate; alicyclic polyisocyanate
such as isophoronediisocyanate and cyclohexylmethanediisocyanate; aromatic diisocyanate
such as tolylenedisocyanate and diphenylmethanediisocyanate; aromatic aliphatic diisocyanate
such as α, α, α', α'-tetramethylxylylenediisocyanate; isocyanurate; the above-mentioned
polyisocyanate blocked with phenol derivatives, oxime and caprolactam; and their combinations.
[0059] The PIC is mixed with polyester such that an equivalent ratio ( [NCO] / [OH] ) between
an isocyanate group [NCO] and polyester having a hydroxyl group [OH] is typically
from 5/1 to 1/1, preferably from 4/1 to 1.2/1 and more preferably from 2.5/1 to 1.5/1.
When [NCO] / [OH] is greater than 5, low temperature fixability of the resultant toner
deteriorates. When [NCO] has a molar ratio less than 1, a urea content in ester of
the modified polyester decreases and hot offset resistance of the resultant toner
deteriorates.
[0060] The polyester prepolymer (A) preferably includes a polyisocyanate group of from 0.5
to 40% by weight, more preferably from 1 to 30% by weight, and furthermore preferably
from 2 to 20% by weight. When the content is less than 0.5% by weight, hot offset
resistance of the resultant toner deteriorates, and in addition, the heat resistance
and low temperature fixability of the toner also deteriorate. In contrast, when the
content is greater than 40% by weight, low temperature fixability of the resultant
toner deteriorates.
[0061] The number of the isocyanate groups included in a molecule of the polyester prepolymer
(A) is at least 1, preferably from 1. 5 to 3 on average, and more preferably from
1.8 to 2.5 on average. When the number of the isocyanate group is less than 1 per
1 molecule, the molecular weight of the urea-modified polyester decreases and hot
offset resistance of the resultant toner deteriorates.
[0062] Specific examples of the amines (B) reacted with the polyester prepolymer (A) include
diamines (B1), polyamines (B2) having three or more amino groups, amino alcohols (B3),
amino mercaptans (B4), amino acids (B5) and blocked amines (B6) in which the amines
(B1-B5) mentioned above are blocked.
[0063] Specific examples of the diamines (B1) include aromatic diamines (e.g., phenylene
diamine, diethyltoluene diamine and 4,4' -diaminodiphenyl methane); alicyclic diamines
(e.g., 4,4'-diamino-3,3'-dimethyldicyclohexyl methane, diaminocyclohexane and isophoronediamine);
aliphatic diamines (e.g., ethylene diamine, tetramethylene diamine and hexamethylene
diamine); etc. Specific examples of the polyamines (B2) having three or more amino
groups include diethylene triamine,triethylene tetramine. Specific examples of the
amino alcohols (B3) include ethanol amine and hydroxyethyl aniline. Specific examples
of the amino mercaptan (B4) include aminoethyl mercaptan and aminopropyl mercaptan.
Specific examples of the amino acids (B5) include amino propionic acid and amino caproic
acid. Specific examples of the blocked amines (B6) include ketimine compounds which
are prepared by reacting one of the amines B1-B5 mentioned above with a ketone such
as acetone, methyl ethyl ketone and methyl isobutyl ketone; oxazoline compounds, etc.
Among these amines (B), diamines (B1) and mixtures in which a diamine is mixed with
a small amount of a polyamine (B2) are preferably used.
[0064] A mixing ratio (i.e., a ratio [ NCO] /[ NHx] ) of the content of the prepolymer (A)
having an isocyanate group to the amine (B) is from 1/2 to 2/1, preferably from 1.
5/1 to 1/1.5 and more preferably from 1.2/1 to 1/1.2. When the mixing ratio is greater
than 2 or less than 1/2, molecular weight of the urea-modified polyester decreases,
resulting in deterioration of hot offset resistance of the toner.
[0065] The urea-modified polyester may include a urethane bonding as well as a urea bonding.
The molar ratio (urea/urethane) of the urea bonding to the urethane bonding is from
100/0 to 10/90, preferably from 80/20 to 20/80 and more preferably from 60/40 to 30/70.
When the content of the urea bonding is less than 10%, hot offset resistance of the
resultant toner deteriorates. The urea-modified polyester can be prepared by a method
such as a one-shot method. The PO and PC are heated at from 150 to 280°C in the presence
of a known esterification catalyst such as tetrabutoxytitanate and dibutyltinoxide
and removing produced water while optionally depressurizing to prepare polyester having
a hydroxyl group. Next, the polyisocyanate is reacted with the polyester at from 40
to 140°C to form a polyester prepolymer (A) having an isocyanate group. Further, the
amines (B) are reacted with the (A) at from 0 to 140°C to form a urea-modified polyester.
[0066] When the PIC, and (A) and (B) are reacted, a solvent may optionally be used. Specific
examples of the solvents include inactive solvents with the PIC such as aromatic solvents
such as toluene and xylene; ketones such as acetone, methyl ethyl ketone and methyl
isobutyl ketone; esters such as ethyl acetate; amides such as dimethylformamide and
dimethylacetamide; and ethers such as tetrahydrofuran.
[0067] A reaction terminator can optionally be used in the crosslinking and/or elongation
reaction between the (A) and (B) to control a molecular weight of the resultant urea-modified
polyester. Specific examples of the reaction terminators include monoamines such as
diethylamine, dibutylamine, butylamine and laurylamine; and their blocked compounds
such as ketimine compounds.
[0068] The weight-average molecular weight of the urea-modified polyester is not less than
10,000, preferably from 20,000 to 10, 000, 000 and more preferably from 30, 000 to
1, 000, 000. When the weight-average molecular weight is less than 10,000, hot offset
resistance of the resultant toner deteriorates. The number-average molecular weight
of the urea-modified polyester is not particularly limited when the after-mentioned
unmodified polyester resin is used in combination. Namely, the weight-average molecular
weight of the urea-modified polyester resins has priority over the number-average
molecular weight thereof. However, when the urea-modified polyester is used alone,
the number-average molecular weight is from 2,000 to 15, 000, preferably from 2, 000
to 10,000 and more preferably from 2,000 to 8,000. When the number-average molecular
weight is greater than 20,000, the low temperature fixability of the resultant toner
deteriorates, and in addition the glossiness of full color images deteriorates.
[0069] A combination of the urea-modified polyester and the unmodified polyester improves
low temperature fixability of the resultant toner and glossiness of color images produced
thereby, and is more preferably used than using the urea-modified polyester alone.
Further, the unmodified polyester may include modified polyester except for the urea-modified
polyester.
[0070] It is preferable that the urea-modified polyester at least partially mixes with the
unmodified polyester to improve the low temperature fixability and hot offset resistance
of the resultant toner. Therefore, the urea-modified polyester preferably has a structure
similar to that of the unmodified polyester.
[0071] A mixing ratio between the unmodified polyester and urea-modified polyester is from
20/80 to 95/5, preferably from 70/30 to 95/5, more preferably from 75/25 to 95/5,
and even more preferably from 80/20 to 93/7. When the urea-modified polyester is less
than 5%, the hot offset resistance deteriorates, and in addition, it is disadvantageous
to have both high temperature preservability and low temperature fixability.
[0072] The binder resin including the unmodified polyester and urea-modified polyester preferably
has a glass transition temperature (Tg) of from 45 to 65°C, and preferably from 45
to 60°C. When the glass transition temperature is less than 45°C, the high temperature
preservability of the toner deteriorates. When higher than 65°C, the low temperature
fixability deteriorates.
[0073] As the urea-modified polyester is likely to be present on a surface of the parent
toner, the resultant toner has better heat resistance preservability than known polyester
toners even though the glass transition temperature of the urea-modified polyester
is low.
[0074] Specific examples of the colorants for use in the present invention include any known
dyes and pigments such as carbon black, Nigrosine dyes, black iron oxide, NAPHTHOL
YELLOW S, HANSA YELLOW (10G, 5G and G), Cadmium Yellow, yellow iron oxide, loess,
chrome yellow, Titan Yellow, polyazo yellow, Oil Yellow, HANSA YELLOW (GR, A, RN and
R), Pigment Yellow L, BENZIDINE YELLOW (G and GR), PERMANENT YELLOW (NCG), VULCAN
FAST YELLOW (5G and R), Tartrazine Lake, Quinoline Yellow Lake, ANTHRAZANE YELLOW
BGL, isoindolinone yellow, red iron oxide, red lead, orange lead, cadmium red, cadmium
mercury red, antimony orange, Permanent Red 4R, Para Red, Fire Red, p-chloro-o-nitroaniline
red, Lithol Fast Scarlet G, Brilliant Fast Scarlet, Brilliant Carmine BS, PERMANENT
RED (F2R, F4R, FRL, FRLL and F4RH), Fast Scarlet VD, VULCAN FAST RUBINE B, Brilliant
Scarlet G, LITHOL RUBINE GX, Permanent Red F5R, Brilliant Carmine 6B, Pigment Scarlet
3B, Bordeaux 5B, Toluidine Maroon, PERMANENT BORDEAUX F2K, HELIO BORDEAUX BL, Bordeaux
10B, BON MAROON LIGHT, BON MAROON MEDIUM, Eosin Lake, Rhodamine Lake B, Rhodamine
Lake Y, Alizarine Lake, Thioindigo Red B, Thioindigo Maroon, Oil Red, Quinacridone
Red, Pyrazolone Red,polyazored, Chrome Vermilion, Benzidine Orange, perynone orange,
Oil Orange, cobalt blue, cerulean blue, Alkali Blue Lake, Peacock Blue Lake, Victoria
Blue Lake, metal-free Phthalocyanine Blue, Phthalocyanine Blue, Fast Sky Blue, INDANTHRENEBLUE
(RS and BC), Indigo, ultramarine, Prussianblue, Anthraquinone Blue, Fast Violet B,
Methyl Violet Lake, cobalt violet, manganese violet, dioxane violet, Anthraquinone
Violet, ChromeGreen, zincgreen, chromiumoxide, viridian, emeraldgreen, Pigment Green
B, Naphthol Green B, Green Gold, Acid Green Lake, Malachite Green Lake, Phthalocyanine
Green, Anthraquinone Green, titanium oxide, zinc oxide, lithopone and the like. These
materials are used alone or in combination. The toner particles preferably include
the colorant in an amount of from 1 to 15% by weight, and more preferably from 3 to
10% by weight.
[0075] The colorant for use in the present invention can be used as a masterbatch pigment
when combined with a resin. Specific examples of the resin for use in the masterbacth
pigment or for use in combination with masterbacth pigment include the modified and
unmodified polyester resins mentioned above; styrene polymers and substituted styrene
polymers such as polystyrene, poly-p-chlorostyrene and polyvinyltoluene; or their
copolymers with vinyl compounds; polymethyl methacrylate, polybutylmethacrylate, polyvinyl
chloride, polyvinyl acetate, polyethylene, polypropylene, polyesters, epoxy resins,
epoxy polyol resins, polyurethane resins, polyamide resins, polyvinyl butyral resins,
acrylic resins, rosin, modified rosins, terpene resins, aliphatic or alicyclic hydrocarbon
resins, aromatic petroleum resins, chlorinated paraffin, paraffin waxes, etc. These
resins are used alone or in combination.
[0076] Specific examples of the charge controlling agent include known charge controlling
agents such as Nigrosine dyes, triphenylmethane dyes, metal complex dyes including
chromium, chelate compounds of molybdic acid, Rhodamine dyes, alkoxyamines, quaternary
ammonium salts (including fluorine-modified quaternary ammonium salts), alkylamides,
phosphor and compounds including phosphor, tungsten and compounds including tungsten,
fluorine-containing activators, metal salts of salicylic acid, salicylic acid derivatives,
etc. Specific examples of the marketed products of the charge controlling agents include
BONTRON 03 (Nigrosine dyes), BONTRON P-51 (quaternary ammonium salt), BONTRON S-34
(metal-containing azo dye), E-82 (metal complex of oxynaphthoic acid), E-84 (metal
complex of salicylic acid), and E-89 (phenolic condensation product), which are manufactured
by Orient Chemical Industries Co., Ltd.; TP-302 and TP-415 (molybdenum complex of
quaternary ammonium salt), which are manufactured by Hodogaya Chemical Co., Ltd.;
COPY CHARGE PSY VP2038 (quaternary ammonium salt), COPY BLUE (triphenyl methane derivative),
COPY CHARGE NEG VP2036 and NX VP434 (quaternary ammonium salt), which are manufactured
by Hoechst AG; LRA-901, and LR-147 (boron complex), which are manufactured by Japan
Carlit Co., Ltd.; copper phthalocyanine, perylene, quinacridone, azo pigments and
polymers having a functional group such as a sulfonate group, a carboxyl group, a
quaternary ammonium group, etc. Among these materials, materials negatively charging
a toner are preferably used.
[0077] The content of the charge controlling agent is determined depending on the species
of the binder resin used, whether or not an additive is added and toner manufacturing
method (such as dispersion method) used, and is not particularly limited. However,
the content of the charge controlling agent is typically from 0.1 to 10 parts by weight,
and preferably from 0.2 to 5 parts by weight, per 100 parts by weight of the binder
resin included in the toner. When the content is too high, the toner has too large
charge quantity, and thereby the electrostatic force of a developing roller attracting
the toner increases, resulting in deterioration of the fluidity of the toner and decrease
of the image density of toner images.
[0078] A wax for use in the toner of the present invention as a release agent has a low
melting point of from 50 to 120°C. When such a wax is included in the toner, the wax
is dispersed in the binder resin and serves as a release agent at a location between
a fixing roller and the toner particles. Thereby, hot offset resistance can be improved
without applying an oil to the fixing roller used. Specific examples of the release
agent include natural waxes such as vegetable waxes, e.g., carnauba wax, cotton wax,
Japan wax and rice wax; animal waxes, e.g., bees wax and lanolin; mineral waxes, e.g.,
ozokerite and ceresine; and petroleum waxes, e.g., paraffin waxes, microcrystalline
waxes and petrolatum. In addition, synthesized waxes can also be used. Specific examples
of the synthesized waxes include synthesized hydrocarbon waxes such as Fischer-Tropsch
waxes and polyethylene waxes; and synthesized waxes such as ester waxes, ketone waxes
and ether waxes. In addition, fatty acid amides such as 1,2-hydroxylstearic acid amide,
stearic acid amide and phthalic anhydride imide; and low molecular weight crystalline
polymers such as acrylic homopolymer and copolymers having a long alkyl group in their
side chain, e.g., poly-n-stearyl methacrylate, poly-n-laurylmethacrylate and n-stearyl
acrylate-ethyl methacrylate copolymers, can also be used. These charge controlling
agent and release agents can be dissolved and dispersed after kneaded upon application
of heat together with a master batch pigment and a binder resin, and can be added
when directly dissolved or dispersed in an organic solvent.
[0079] The toner particles are preferably mixed with an external additive to assist in improving
the fluidity, developing property and charging ability of the toner particles. Suitable
external additives include inorganic particulate materials. It is preferable for the
inorganic particulate materials to have a primary particle diameter of from 5 nm to
2 µm, and more preferably from 5 nm to 500 nm. In addition, it is preferable that
the specific surface area of such particulate inorganic materials measured by a BET
method is from 20 to 500 m
2/g. The content of the external additive is preferably from 0.01 to 5% by weight,
and more preferably from 0.01 to 2.0% by weight, based on total weight of the toner
composition. Specific examples of such inorganic particulate materials include silica,
alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontiumtitanate,
zinc oxide, tin oxide, quartz sand, clay, mica, sand-lime, diatomearth, chromiumoxide,
ceriumoxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide,
barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride,
etc. Among these particulate inorganic materials, a combination of a hydrophobic silica
and a hydrophobic titanium oxide is preferably used. In particular, when a hydrophobic
silica and a hydrophobic titanium oxide each having an average particle diameter not
greater than 50 nm are used as an external additive, the electrostatic force and van
der Waals' force between the external additive and the toner particles are improved,
and thereby the resultant toner composition has a proper charge quantity. In addition,
even when the toner composition is agitated in a developing device, the external additive
is hardly released from the toner particles, and thereby image defects such as white
spots and image omissions are hardly produced. Further, the quantity of particles
of the toner composition remaining on image bearing members can be reduced.
[0080] When particulate titanium oxides are used as an external additive, the resultant
toner composition can stably produce toner images having a proper image density even
when environmental conditions are changed. However, the charge rising properties of
the resultant toner tend to deteriorate. Therefore the addition quantity of a particulate
titanium oxide is preferably smaller than that of a particulate silica, and in addition
the total addition amount thereof is preferably from 0.3 to 1.5% by weight based on
weight of the toner particles not to deteriorate the charge rising properties and
to stably produce good images.
[0081] A method of preparing the toner of the present invention is explained, but is not
limited thereto.
(1) Dispersing a colorant, an unmodified polyester, a polyester prepolymer having
an isocyanate group and a wax in an organic solvent to prepare a toner constituents
liquid.
The organic solvent is preferably volatile, having a boiling point less than 100°C
because of being easily removed after parent toner particles are formed. Specific
examples of the organic solvent include toluene, xylene, benzene, carbon tetrachloride,
methylenechloride, 1,2-dichloroethane, 1,1,2-trichloroethane, trichloroethylene, chloroform,
monochlorobenzene, dichloroethylidene, methylacetate, ethylacetate, methyl ethyl ketone,
methylisobutylketone, etc. These can be used alone or in combination. Particularly,
aromatic solvents such as toluene and xylene and halogenated hydrocarbons such as
methylenechloride, 1,2-dichloroethane, chloroform and carbon tetrachloride are preferably
used. The toner constituents liquidpreferably includes an organic solvent in an amount
of from 0 to 300 parts by weight, more preferably from 0 to 100 parts by weight, and
furthermore preferably from 25 to 70 parts by weight per 100 parts by weight of the
prepolymer.
(2) Emulsifying the toner constituents liquid in an aqueous mediumunder the presence
of a surfactant and a particulate resin. The aqueous medium may include water alone
and mixtures of water with a solvent which can be mixed with water. Specific examples
of the solvent include alcohols such as methanol, isopropanol and ethylene glycol;
dimethylformamide; tetrahydrofuran; cellosolves such as methyl cellosolve; and lower
ketones such as acetone and methyl ethyl ketone.
The toner constituents liquid preferably includes the aqueous medium is typically
from 50 to 2,000 parts by weight, and preferably from 100 to 1,000 parts by weight.
When less than 50 parts by weight, the toner constituents liquid is not well dispersed
and toner particles having a predetermined particle diameter cannot be formed. When
greater than 2,000 parts by weight, the production cost increases.
A dispersant such as a surfactant or an organic particulate resin is optionally included
in the aqueous medium to improve the dispersion therein.
Specific examples of the surfactants include anionic surfactants such as alkylbenzene
sulfonic acid salts, α-olefin sulfonic acid salts, and phosphoric acid salts; cationic
surfactants such as amine salts (e.g., alkyl amine salts, aminoalcohol fatty acid
derivatives, polyamine fatty acid derivatives and imidazoline), and quaternary ammonium
salts (e.g., alkyltrimethyl ammonium salts, dialkyldimethyl ammonium salts, alkyldimethyl
benzyl ammonium salts, pyridinium salts, alkylisoquinolinium salts and benzethonium
chloride);nonionic surfactants such as fatty acid amide derivatives, polyhydric alcohol
derivatives; and ampholytic surfactants such as alanine, dodecyldi(aminoethyl)glycin,
di(octylaminoethyle) glycin, and N-alkyl-N,N-dimethylammonium betaine.
A surfactant having a fluoroalkyl group can prepare a dispersion having good dispersibility
even when a small amount of the surfactant is used. Specific examples of anionic surfactants
having a fluoroalkyl group include fluoroalkyl carboxylic acids having from 2 to 10
carbon atoms and their metal salts, disodium perfluorooctanesulfonylglutamate, sodium
3-{omega-fluoroalkyl(C6-C11)oxy}-1-alkyl(C3-C4) sulfonate, sodium-{omega-fluoroalkanoyl(C6-C8)-N-ethylamino}-1-propane
sulfonate, fluoroalkyl(C11-C20) carboxylic acids and their metal salts, perfluoroalkylcarboxylic
acids and their metal salts, perfluoroalkyl(C4-C12)sulfonate and their metal salts,
perfluorooctanesulfonic acid diethanol amides, N-propyl-N-(2-hydroxyethyl)perfluorooctanesulfone
amide, perfluoroalkyl(C6-C10)sulfone amide propyltrimethylammonium salts, salts of
perfluoroalkyl(C6-C10)-N-ethylsulfonylglycin, monoperfluoroalkyl(C6-C16)ethylphosphates,
etc.
Specific examples of the marketed products of such surfactants having a fluoroalkyl
group include SURFLON S-111, S-112 and S-113, which are manufactured by Asahi Glass
Co., Ltd. ; FRORARD FC-93, FC-95, FC-98 and FC-129, which are manufactured by Sumitomo
3M Ltd.; UNIDYNE DS-101 and DS-102, which are manufactured by Daikin Industries, Ltd.;
MEGAFACE F-110, F-120, F-113, F-191, F-812 and F-833 which are manufactured by Dainippon
Ink and Chemicals, Inc.; ECTOP EF-102, 103, 104, 105, 112, 123A, 306A, 501, 201 and
204, which are manufactured by Tohchem Products Co., Ltd.; FUTARGENT F-100 and F150
manufactured by Neos; etc.
Specific examples of cationic surfactants, which can disperse an oil phase including
toner constituents in water, include primary, secondary and tertiary aliphatic amines
having a fluoroalkyl group, aliphatic quaternary ammonium salts such as erfluoroalkyl(C6-C10)sulfoneamide
propyl trimethylammonium salts, benzalkonium salts, benzetonium chloride, pyridinium
salts, imidazolinium salts, etc. Specific examples of the marketed products thereof
include SURFLON S-121 (from Asahi Glass Co., Ltd.); FRORARD FC-135 (from Sumitomo
3M Ltd.); UNIDYNE DS-202 (from Daikin Industries, Ltd.) ; MEGAFACE F-150 and F-824
(from Dainippon Ink and Chemicals, Inc.); ECTOP EF-132 (from Tohchem Products Co.,
Ltd.); FUTARGENT F-300 (from Neos); etc.
The particulate resin is included to stabilize a parent toner particles formed in
the aqueous medium. Therefore, the particulate resin is preferably included so as
to have a coverage of from 10 to 90% over a surface of the toner particle. Specific
examples of the particulate resins include particulate polymethylmethacrylate having
a particle diameter of 1 µm and 3 µm, particulate polystyrene having a particle diameter
of 0.5 µm and 2 µm and a particulate polystyrene-acrylonitrile having a particle diameter
of 1 µm. These are marketed as PB-200 from Kao Corporation, SGP from Soken Chemical
& Engineering Co., Ltd. , Technopolymer SB from Sekisui Plastics Co., Ltd., SGP-3G
from Soken Chemical & Engineering Co., Ltd. and Micro Pearl from Sekisui Chemical
Co., Ltd.
In addition, inorganic dispersants such as tricalcium phosphate, calcium carbonate,
titanium oxide, colloidal silica and hydroxy apatite can also be used.
As dispersants which can be used in combination with the above-mentioned particulate
resin and inorganic dispersants, it is possible to stably disperse toner constituents
in water using a polymeric protection colloid. Specific examples of such protection
colloids include polymers and copolymers prepared using monomers such as acids (e.g.,
acrylic acid, methacrylic acid, α-cyanoacrylic acid, α-cyanomethacrylic acid, itaconic
acid, crotonic acid, fumaric acid, maleic acid and maleic anhydride), acrylic monomers
having a hydroxyl group (e.g., β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate,
β-hydroxypropyl acrylate, β-hydroxypropyl methacrylate, γ-hydroxypropyl acrylate,
γ-hydroxypropyl methacrylate, 3-chloro-2-hydroxypropyl acrylate, 3-chloro-2-hydroxypropyl
methacrylate, diethyleneglycolmonoacrylic acid esters, diethyleneglycolmonomethacrylic
acid esters, glycerinmonoacrylic acid esters, N-methylolacrylamide and N-methylolmethacrylamide),
vinyl alcohol and its ethers (e.g., vinyl methyl ether, vinyl ethyl ether and vinyl
propyl ether), esters of vinyl alcohol with a compound having a carboxyl group (i.e.,
vinyl acetate, vinyl propionate and vinyl butyrate); acrylic amides (e.g, acrylamide,
methacrylamide and diacetoneacrylamide) and their methylol compounds, acid chlorides
(e.g., acrylic acid chloride and methacrylic acid chloride), and monomers having a
nitrogen atom or an alicyclic ring having a nitrogen atom (e.g., vinyl pyridine, vinyl
pyrrolidone, vinyl imidazole and ethyleneimine). In addition, polymers such as polyoxyethylene
compounds (e.g., polyoxyethylene, polyoxypropylene, polyoxyethylenealkyl amines, polyoxypropylenealkyl
amines, polyoxyethylenealkyl amides, polyoxypropylenealkyl amides, polyoxyethylene
nonylphenyl ethers, polyoxyethylene laurylphenyl ethers, polyoxyethylene stearylphenyl
esters, and polyoxyethylene nonylphenyl esters); and cellulose compounds such as methyl
cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose, can also be used as
the polymeric protective colloid.
The dispersion method is not particularly limited, and low speed shearing methods,
high-speed shearing methods, frictionmethods, high-pressure jetmethods, ultrasonic
methods, etc. can be used. Among these methods, high-speed shearing methods are preferably
used because particles having a particle diameter of from 2 to 20 µm can be easily
prepared. At this point, the particle diameter (2 to 20 µm) means a particle diameter
of particles including a liquid). When a high-speed shearing type dispersion machine
is used, the rotation speed is not particularly limited, but the rotation speed is
typically from 1,000 to 30,000 rpm, and preferably from 5,000 to 20,000 rpm. The dispersion
time is not also particularly limited, but is typically from 0.1 to 5 minutes. The
temperature in the dispersion process is typically from 0 to 150°C (under pressure),
and preferably from 40 to 98°C.
3) While an emulsion is prepared, amines (B) are included therein to be reacted with
the polyester prepolymer (A) having an isocyanate group.
This reaction is accompanied by a crosslinking and/or a elongation of a molecular
chain. The reaction time depends on reactivity of an isocyanate structure of the prepolymer
(A) and amines (B), but is typically from 10 min to 40 hrs, and preferably from 2
to 24 hrs. The reaction temperature is typically from 0 to 150°C, and preferably from
40 to 98°C. In addition, a known catalyst such as dibutyltinlaurate and dioctyltinlaurate
can be used.
After the reaction is terminated, an organic solvent is removed from an emulsified
dispersion (a reactant), which is washed and dried to form a parent toner particle.
The prepared emulsified dispersion (reactant) is gradually heated while stirred in
a laminar flow, and an organic solvent is removed from the dispersion after stirred
strongly when the dispersion has a specific temperature to form a parent toner particle
having the shape of a spindle. When an acid such as calcium phosphate or a material
soluble in alkaline is used as a dispersant, the calcium phosphate is dissolved with
an acid such as a hydrochloric acid and washed with water to remove the calcium phosphate
from the toner particle. Besides this method, it can also be removed by an enzymatic
hydrolysis.
5) A charge controlling agent is beaten in the parent toner particle, and inorganic
particulate materials such as particulate silica and particulate titanium oxide are
externally added thereto to form a toner.
[0082] Known methods using a mixer, etc. are used to beat in the charge controlling agent
and to externally add the inorganic particulate materials.
[0083] Thus, a toner having a small particle diameter and a sharp particle diameter distribution
can be obtained. Further, the strong agitation in the process of removing the organic
solvent can control the shape of a toner from a sphere to a rugby ball, and the surface
morphology thereof from being smooth to a pickled plum.
[0084] The toner for use in the present invention has the shape of almost a sphere, which
can be specified as follows. Fig. 11A is an external view of the toner, and Figs.
11B and 11C are cross sections of the toner, wherein the toner preferably satisfies
the following relationship:
wherein r
1, r
2 and r
3 represent the average major axis particle diameter, the average minor axis particle
diameter and the average thickness of particles of the toner respectively, and wherein
r
3 ≤ r
2 ≤ r
1.
[0085] When the ratio (r
2/r
1) is too small, the toner has a form far away from the spherical form, and therefore
the toner has poor dot reproducibility and transferability, resulting in deterioration
of the image quality. When the ratio (r
3/r
2) is too small, the toner has a form far away from the spherical form, and therefore
the toner has poor transferability. When the ratio (r
3/r
2) is 1.0, the toner has a form similar to the spherical form, and therefore the toner
has good fluidity.
[0086] The above-mentioned size factors (i.e., r
1, r
2 and r
3) of toner particles can be determined as follows:
uniformly dispersing the toner on a smooth measuring surface;
observing 100 toners with a color laser microscope VK-8500 from Keyence Corp. at 500
magnifications to measure r1, r2 and r3 thereof; and
averaging them.
[0087] The toner prepared by polymerization methods has the shape of almost a sphere and
a small particle diameter, but has lightly poor mixability and dispersibility with
a developer in an image developer.
[0088] However, as shown in Figs. 1 and 2, the image developer having three screws, i.e.,
the feeding screw 4, the collection screw 5 and the stirring transfer screw 6 which
are functionally-independent largely improves the mixability and dispersibility of
a toner having the shape of almost a sphere and a small particle diameter.
[0089] Further, the toner concentration sensor 15 detects the toner consumption, i.e., an
amount of the toner required on a downstream side of the collection screw 5 to drive
a toner feeder in real time. Therefore, the developer including even the toner prepared
by polymerization methods, which is likely to be insufficiently mixed in the stirring
transfer section 9 and the stirring transfer screw 6 has a stable toner concentration.
As a result, the image developer produces images without uneven image density.
[0090] The present invention provides an image developer and an image forming apparatus
capable of improving the dispersibility of a developer even including a toner having
poor mixability and dispersibility, and precisely detecting the toner concentration
to prevent uneven toner concentration of the developer and uneven image density. In
addition, the image developer and image forming apparatus produce images without toner
scattering or background fouling due to repeated excessive supplies of a toner, using
a wide range of toners.
[0091] This is not only the case where the feeding screw is above the collection screw in
Fig. 1, but also the case where the collection screw with a toner concentration sensor
on a downstream side thereof is above the feeding screw.
[0092] The developer for use in the present invention is typically a two-component developer
including a magnetic carrier and a non-magnetic toner. However, the developer is not
limited thereto and other two-component developers, e.g., including a magnetic carrier
and a magnetic toner can be used therein.